Electromagnetic audio amplifier



Oct. 27, 1953 w. GLKLUZ 2,657,281

ELECTROMAGNETIC AUDIO AMPLIFIER Filed Feb. 15', 1950 2,Sheets-Sheet 1 INVENTOR. flu 727? 6'. /fiz/z BY Oct. 27, 1953 w. c. KLUZ ELECTROMAGNETIC AUDIO AMPLIFIER 2 Sheets-Sheet 2 Filed Feb. 15,- 1950 INVENTOR #494756 5/6102 M I97'7U/4P/VEV ZLW Fatented Oct. 27, 1953 ELECTROMAGNETIC AUDIO AMPLIFIER Walter C. Kluz, Yonkers, N. Y., assignor to Ward Leonard Electric Company, a corporation of New York Application February 15, 1950, Serial No. 144,339

3 Claims. 1

This invention relates to electromagnetic audio amplifiers wherein any form of signal or imposed control within the audio range may be greatly amplified. It is particularly applicable to voice amplification but is desirable for many other uses.

The main objects are to avoid the use of vacuum tubes and to produce a simplified form of apparatus which will have no moving parts and be durable and dependable under long continued use. Another important object i to improve the fidelity of reproduction of the amplified output. Other objects and advantages will be understood from the following description and accompanying drawing showing a preferred embodiment of the invention.

Fig. 1 is a diagram showing the apparatus, relationship of parts and connections for obtaining one stage of amplification; and Fig. 2 is a similar diagram showing two stages of amplification.

Referring to Fig. 1, there are shown four reactors of the self-saturating type having laminated circular cores A, B, C and D. On each of these cores isa main or anode windin la, lb, I and id respectively. Each core also has a controlling winding 2a, 2b, 2c and 2d respectively; and also abiasing winding 3a, 3b, 3c and lid respectively.

Each main or anode winding is supplied with current from an alternating current source 4 through a transformer having a primary wind- 7 ing 5 and a secondary winding 5a. The source is of approximately constant potential and has a high frequency, such as 10,000 cycles or more, and at least several times the highest audio frequency to be amplified for good reproduction. The voltage supplied to the main windings of the reactors from the secondary 5a maybe of the order of 256 volts depending on the size of the reactors and number of turns in the main,

windings.

fihe lower terminal of the secondary 5aof the source is shown connected tothe mainwinding is. The upper terminal of the secondary 5a is shown connected to the main winding id. This results in full wave rectified current being supplied-to the upper half of the primary 7 of an output transformer. Similarly the lower terminal of the secondary 5a is shown connected to the main winding ib, and the upper terminal to the main winding lc. This similarly results in full wave rectifiedcurrent being supplied to the lower half of the primary '5 of the output transformer. The return path of these full wave currents is from the mid-point of the winding t the mid-point of the winding 5a. The net windings;

result of the components of these rectified currents through the two halves of the winding 3 in opposite directions to each other, is that the magneto-motive forces of these currents are in opposition and produce no resultant flux in the core of the output transformer. Thus no voltage is induced in the secondary winding la of the output transformer due to these primary currents provided all the components are in balance electrically and magnetically.

In the lower left-hand portion of Fig. 1 is shown a source of variable audio frequency current Waves comprising a carbon microphone transmitter 8 in circuit with a direct current source indicated as a battery 9. Current therefrom is supplied to the primary winding at or" a transformer having ,a secondary winding Ella which supplies current through a network consistins of a capacitor H and an inductor Ha in series with each other, the capacitorv being shunted by a resistor ill). The purpose of this network is first, to approach a linear response between signal frequency and the output of the amplifier; and second, to limit the circulating current in the signal circuit. From this network the circuit continues through the controllin windings 2a, 2b, 2c and 2d of the reactors. These windings are connected in series with each other but are relatively connected, as shown in Fig. 1, so that the effect of the magnetomotive force of the winding 2b on the main flux of the core B is opposite to the efiect of the magnetomotive force of the'winding 2a onthe main flux of the core A; and likewise the magnetomotive force of the winding 2d on the main flux of the core D is opposite to the effect of the magnetomotive force of the winding 2c on the main flux of the core C. I

The output current of the main or anode windings varies accordin to'their change of impedance and the control windings serve-to vary their impedance in accordance with the change in value and direction of the currents in the control If a curve be plotted with abscissas indicating the ampere turns of the control windings and with ordinates, representing the full wave output voltage or current of a pair of the main windings, it will show a very pronounced increase or decrease in the output voltage with a comparatively small increase or decrease in the pere turns of the control windings. This region of pronounced changeioccurs not: only when the magnetomotive force of a control winding acts with that of a main winding'but also when in opposition thereto although to a lesser extent.

If the magnetization of the cores be adjusted so that the output voltage of the main windings as influenced by the control windings is within this region of pronounced change, then the best results in pronounced and amplified change of the output of the main windings are obtained. It is the function of th'ebiasin'g windings 3a, 3b, 3c and 302 to bring the operation Within this region by adjustment of the current in the biasing windings. It is desirable to makethisadjustment to bring the operating point when no signal is present at the mid-point of the abovementioned curve. A operation and less affect on the regulation of the power carrier source. Fig. =1-shows these biasing windings connected in series with each other and supplied by a direct currentsourde 1-2 through an adjustable resistive device l3 and a filter choke 13a. This choke limits the circulating current-in the biasing circuit. In viewof the fact that each of the cores should have a similar adjustment of flux-condition for operation in the region of pronounced change, the magnetomotive force of each of the biasing windings has the same relation to the magnetomotive force of each of the 'main windings as indicated by the connections shown in Fig. 1. In cases where the design of the main windings and core are such as to result in Class A operation over the region of pronounced changethe biasing windings may be omitted.

The secondary winding 'ia'of the output transformer supplies current to a loud speaker 14. A variable'resistor i5 is shown connected across the terminals of the secondary 70a for by-passing a portion of the output power of the amplifier in case the loudspeaker cannot withstand the full output power. A capacitor I6 is connected between each of the terminals of the primary winding 7 and its mid-connection for by-pass'ing the high frequency ripple of the rectified carrier wave.

In operation, the high frequency currents from the source 4 'pass through the main or anode windings la, lb, lo and l d to their respective rectifiers 6a, so, 60 and 6d. The output current or voltage from the main windings and rectifiers is modified in accordance with the variations of the audio signal currents of the control windings by affecting the impedance of the main windings.

When an audio signal in a positive direction passes through the control windings, it causes an increase in the impedance of the anode windings la and Id and a decrease in the impedance of the anode windings lb and 10 by virtue of the relation of the polarities of the magnetomotive forces of the'control windings with'reference to the polarities of the magnetomotive forces of the anode windings. This result in modifying the full wave currents in the primary 1 as affected by the changes in the signalourrents to produce the wave shape or pattern of the s gnal currents in the winding 7a of the output transformer. When an audio signal in a negative directionpasses through the control windings, the action is the same except in a reversed sense. Thus'the overall result is an amplified reproduction in the loud speaker of the signal wave shape imposed on the control windings.

When signals are present in the control windings, the net 'flux in the core of the output transformer due to the magnetomoti-veforces produced by curent components other than the signal cur- This results in sir-called 'Class :pair-ofreactors areso connected as to cancel the fundamental frequency of the main windings, the

{higher harmonics present result in some circulatingc'ur'ren't inth'e'control circuit. This circulating current tends "to saturate the cores of the reactors to some extent and reduces the power gain. The network serves to reduce this circulatingcurrent but the power dissipated in this series network is a loss which reduces the amplifier gain; but a compromise can-be arrivedat to secure satisfactoryperformance with a ver ygood increase in power amplification. The network also aids the amplifier in producing a more linear a response as already referred to.

Test results on a single stage amplifier as described with reference to Fig. 1 gave very good and clear amplification of the signal frequencies over a range from mete-2500 cycles and almost as good up to 3000-cycles. The power gain from these tests in the audio output compared with the audio input was between 9 and 10 times within the frequency range just mentioned. The frequency of the carrier source these tests was 10,000 cycles. The reactor cores were of a high nickel'steel. The rectifiers were of the dry disk selenium type.

Fig. 2 shows two'stages of amplification, each of the two stages being similar to that described with reference to Fig. 1 and the corresponding parts are similarly designated. In Fig. 2 the output from the secondary winding la of the first stage is supplied to the primary winding I? of an inter-stage transformer having .a secondary winding Ha which in turn serves to supply the control windings of thesecond stage. The main windings of the second stage are supplied from the secondary winding 50 of another transformer having a primary winding 51) supplied from the source l and having their circuits connected similarly to those of thefirst stage. The biasing windings of the second stage are supplied from the direct current source I 2 through an adjustable resistive device it and 'a filter choke [8a. InFig. 2 the amplified current output of variable audio frequencies'from th first stage is delivered to the control windings of 'thesecond stage and there again amplified in the same manner as in the first stage. Additional stages could be provided similarly if desired.

Although the disclosure in the drawings is for controlof the full wave rectification of the high frequency source 'for securing the best results, only half-wave rectification may sometimes be used with satisfactory results according to the particular purpose of use and results desired. With'half-waverectification, only a pair of cores such ash and C or B and D with their windings and connections inaybe used. In that case the mode ofoperation would be similar in some respects to'that already described.

Although separate cores of circular-form have been particularly shown, the cores may have other' 'forms or maybe-combined in'one or more units to obtain the mode of control-and operation as described. Various other modifications may be made for application to particular requirements without departing from the scope of the invention.

I claim:

1. -An electromagnetic amplifier for amplifying audio signals from an audio signal source comprising an input transformer and an output transformer with the midpoints of each of said transformers interconnected, a continuous alternating current source having a frequency higher than the highest audio frequency, a first pair of cores each having a main winding connected to one terminal of said input transformer and a second pair of cores each having a main winding connected to the other terminal of said input transformer, each core having a control winding, said control windings being connected in series to said signal source, the first pair of cores having the relation of the magnetomotive forces of the control winding and the main winding of one core reversed to the relation of the magnetomotive forces of the control winding and main winding of the other core of the first pair, the second pair of cores having the relation of the magnetomotive forces of the control winding and main winding of one core reversed to the relation of the magnetomotive forces of the control winding and main winding of the other core of said second pair of cores, each main winding having a rectifier connected in series therewith and passing current in the same direction, the main windings of the cores of either pair having one relation of the magnetomotive forces being connected through their respective rectifiers to one terminal of the output transformer and the main windings of the cores of either pair having the reverse relation of the magnetomotive forces being connected through their respective rectifiers to the opposite terminal of the output transformer to balance the output under no-signal conditions and creating an amplified difference corresponding to the audio signal under signal conditions.

2. An electromagnetic amplifier for amplifying audio signals from an audio signal source comprising two input terminals adapted to be connected to a continuous alternating current source with a frequency higher than the highest audio frequency and a center terminal between said input terminals, two output terminals for connecting the amplifier to a load and a center terminal between said output terminals, means electrically interconnecting said center terminals, a first pair of cores each having a main winding connected to one input terminal and a second pair of cores each having a main winding connected to the other input terminal, each core having a control winding, said control windings being connected in series to receive an audio signal from the signal source, the first pair of cores having the relation of the magnetomotive forces of the magnetomotive forces of the control winding and main winding of the other core of said second pair of cores, each main winding having a rectifier connected in series therewith and passing current in the same direction, the main windings of the cores of either pair having one relation of the magnetomotive forces being connected through their respective rectifiers to one output terminal and the main windings of the cores of the other pair having the reverse relation of the magnetomotive forces being connected through their respective rectifiers to the other output terminal to balance the output under no-signal conditions and creating an amplified difference corresponding to the audio signal under signal conditions.

3. An electromagnetic amplifier connected between input terminals and output terminals for amplifying audio signals from an audio signal source comprising electrical connecting means including intermediate terminals between the input terminals and the output terminals respectively to provide a current return path between the input and the output for balancing the amplifier, means for compressing a continuous alternating current source having a frequency higher than the highest audio frequency on said input terminals, a first pair of cores each having a main winding connected to one input terminal and a second pair of cores each having a main winding connected to the other input terminal to receive the higher frequency current, each core having a control winding, said control windings being connected to said signal source to vary the impedance of said respective main windings, the first pair of cores having the relation of the magnetomotive forces of the control winding and the main winding of one core reversed to the relation of the magnetomotive forces of the control Winding and the main winding of the other core of the first pair, the second pair of cores having the relation of the magnetomotive forces of the control winding and main winding of one core reversed to the relation of the magnetomotive forces of the control winding and main winding of the other core of said second pair of cores, each main winding having a rectifier connected in series therewith and passing current in the same direction, the main windings of the cores of either pair having one relation of themagnetomotive forces being connected through their respective rectifiers to one output terminal and the main windings of the cores of either pair having the reverse relation of the magnetomotive forces being connected through their respective rectifiers to the other output terminal to balance the output under no-signal conditions and creating an amplified difference corresponding to the audio signal under signal conditions.

WALTER C; KLUZ.

References Cited in the ille al this patent UNITED STATES PATENTS Number Name Date 2,108,642 Boardman Feb. 15, 1938 2,164,383 Burton July 4, 1939 2,338,423 Geyger Jan. 4, 1944 2,464,639 Fitzgerald Mar. 15, 1949 OTHER REFERENCES Magnetic Amplifiers Geyger, A. I. E. E. Misc. Paper 50-93 pp. 10, 11, 22, 23. 

